Communication systems are designed to transfer information between two devices over a medium in the presence of disturbing influences. Intersymbol interference (ISI) is one well-known disturbing influence in which transmitted symbols become elongated and interfere with adjacently transmitted symbols. This spreading or “smearing” of symbols is generally caused by the dispersive nature of common communication mediums. Because ISI has the same effect as noise, including a deleterious effect on bit error rate, communication is made less reliable.
One of the most basic solutions for mitigating the effects of ISI is slowing down the speed at which symbols are transmitted over a medium. More specifically, the transmission speed can be slowed down such that a symbol is only transmitted after allowing previously transmitted symbol pulses to dissipate. The time it takes for a symbol pulse to dissipate is called delay spread, whereas the original time of the symbol pulse (including any time before the next symbol pulse is transmitted) is called the symbol time. No ISI will occur if the delay spread is less than or equal to the symbol time.
Although slowing down the symbol rate can reduce or eliminate the effects of ISI and other sources of noise, it is generally an unacceptable solution for many of today's communication applications. In fact, many of today's communication applications require speeds in the multi-gigabit per second range. At such high speeds, ISI can completely overwhelm a signal transmitted over a few inches of printed circuit board trace, a few feet of copper cable, or a few tens of meters of multimode optical fiber.
As a result, additional signal processing components are now commonly found in many of today's communication devices to combat ISI and other sources of noise so that the symbol rate can be maintained at required rates. For example, the physical layer device (PHY) of a communication device communicating over a channel will often include an adaptive decision feedback equalizer (DFE) to perform post-equalization of the channel to reduce ISI, as well as a forward error correction (FEC) encoder/decoder with a high coding gain to further improve the effective signal-to-noise ratio (SNR) of the channel. Although these additional signal processing components can help to reduce the effects of noise, these components are not without cost. For example, these additional components require additional area, power, and ability to dissipate heat. In communication ends that are congested (e.g., that transmit and/or receive large amounts of data) or that are physically crowded, the added area, power, and heat dissipation requirements can be prohibitive.
The embodiments of the present disclosure will be described with reference to the accompanying drawings. The drawing in which an element first appears is typically indicated by the leftmost digit(s) in the corresponding reference number.